I'm attempting to create an equation for determining an equal ratio between a given number of points across a given distance. However, I am having trouble rearranging the equation to solve for ratio.

D - Distance
R - Ratio
N - Number of points

D = R^1 + ... R^N

For example,

30 = 2^1 + 2^2 + 2^3 + 2^4 = 2 + 4 + 8 + 16

Thanks in advance!